Final Week Drama: A State-by-State Guide to Who Will Win the Senate

Will Mitch McConnell retain his title of Senate Majority Leader when the new Congress gavels into session in January, or will New York DemocratChuck Schumer step into that role? The answer to that question will be determined by a small number of very close races, scattered across the country. Democrats need to net four or five seats to retake the upper chamber, depending on the presidential race's outcome. Let's examine those Senate contests playing out in battleground states (broadly defined), starting with the least competitive races:

Arizona: John McCain looks to be a lock for re-election, despite Hillary Clinton's strong play for the state. His Democratic challenger's strong embrace of Obamacare is...not going well. SolidGOP hold.

Iowa, Georgia, Alaska: GOP incumbents in these bona fide/borderline/potential presidential toss-ups are expected to cruise to re-election, based on public polling. SolidGOP holds.

Colorado: A handful of surveys show the Rocky Mountain state possibly within reach for Trump, but GOP Senate nominee Daryl Glenn has gained almost no traction at all against incumbent Democrat Michael Bennet, who was once considered vulnerable. SolidDemocrat hold.

Ohio: This one was supposed to be a high-stakes barn-burner, but Rob Portman's excellent campaign and incredible resilience has turned it into a snoozer. LikelyGOP hold.

Wisconsin: Ron Johnson's strong campaign has forced Democrats to inject more money into this race, but lock-step liberal Russ Feingold remains the favorite to re-take his old seat. Then again, things may be closing in the waning days. LeanDemocrat pick-up.

Florida: When polls tightened up a bit in recent weeks, some liberals expressed frustrations over national Democrats' decision to pull funds away from Marco Rubio's challenger. But the last four public polls of the race show Rubio ahead by an average of more than six percentage points. The incumbent has never trailed in this race, and Patrick Murphy appears to be sputtering down the stretch. Lean GOP hold.

Nevada: Early voting trends in the Silver State appear to be favoring Democrats so far, and a strong push among Hispanics against Trump (coupled with pro-Trump frustrations over Republican Joe Heck rescinding his support after the Access Hollywood tape emerged) may allow Harry Reid's hand-picked successor to prevail. Heck still has a razor-thin RCP average edge, but internal polls reportedly show Cortez Masto out front by a nose. He's a high-quality candidate, but Nevada is shading blue at the moment -- although Nevadans did elect a Republican Senator in 2012, while also handing Obama a decisive win. We'll call this a (very slight) lean Democrat hold.

Pennsylvania: Pat Toomey has run an impressively robust race, keeping his head above water in the vote-rich Philly suburbs. But his ethically-challenged Democratic challenger has led narrowly in the last three public surveys in a state that appears poised to fall into Hillary Clinton's column. Toomey barelysqueaked by in the Republican wave year of 2010, so pinning his hopes on lots of 2016 ticket-splitters is a tough (albeit plausible) sell. If Trump can perform competitively in the Keystone State, the incumbent Senator has a very real chance of pulling this out. Looking at the overall fundamentals, however, I'm tempted to call this a (very slight) lean Democrat pick-up. But for now, especially with Obamacare and FBI developments, it stays in the toss-up pile.

Missouri: The good news for Republican Roy Blunt is that he represents a red state in which Donald Trump is faring rather well. The bad news is that he still looks vulnerable against a young veteran running as a moderate (but who Republicans argue would be a Clinton rubber-stamp). This one is closer than it should be. Toss-up.

North Carolina:ACLU activist Deborah Ross' far-Left stances have been blared across the airwaves over the past month, allowing GOP incumbent Richard Burr to build a small lead over his challenger. But Hillary Clinton's edge in the Tar Heel State has looked stubbornly stable, meaning that Burr may have to rely on a significant number of crossover voters to survive. Toss-up.

Indiana: The hits keep coming for Evan Bayh, whose double-dealing, cronyism, absenteeism and liberalism are taking a pounding in on-air ads. A new Monmouth poll of the state shows Donald Trump and Hoosier Mike Pence opening up a double-digit lead there, with the Senate race exactly tied. As negative headlines continue to batter Bayh, Republicans sense momentum. Toss up. Here's conservative Todd Young's closing argument-style TV ad, in which he basically promises to be the anti-Bayh:

New Hampshire:National Journal calls this fight the swing-iest of the swing races. Republican Kelly Ayotte owns a small lead, but the state is trending toward Hillary, and Democrats boast superior ground game. If this contest is called early in either direction, that could be a major indicator of how things will play out across the country as election night unfolds. Toss-up. This is the Ayotte campaign's new web ad tying Maggie Hassan to Hillary Clinton's dishonesty and corruption:

Bottom line: If I had to plunk down a cash bet today, I'd say Missouri and North Carolina break to the GOP candidates, while Democrats eke out Nevada and Pennsylvania -- although all four of those races are close enough to go either way. Control of the Senate, therefore, could very well come down to whether Republicans can successfully defend their seats in New Hampshire and Indiana. Those races feel like the purest of the toss-ups. Ultimately, I can envision Republicans holding as many as 51 or 52 seats when the dust settles, or as few as 47 or 48. Running through various scenarios, a 50/50 split may just be the likeliest outcome, meaning that Democrats would hold a nominal majority if the Clinton ticket prevails at the presidential level -- and Republicans would have a shot at recapturing the majority in 2017's Virginia Senate race to fill the seat vacated by Tim Kaine. Before you go, read this Boston Globe exclusive about a massive illegal straw donor scheme, from which most of the Democrats on this list have benefitted. Stay tuned. One week.